This calculator is an example of why
Sharp became so successful in the calculator marketplace, and is one of the
'survivors' today. This little machine was cranked out by the 10's of
thousands (if not more), and was a simple, low-cost, home/office
calculator. This particular machine was built on 7/8/74, based on the
date on the manufacturing tag still in good shape on the bottom of the machine.
The IC's inside have date codes of late '73 to early '74, which
further substantiate the date of manufacture.

Inside View of ELSI 817S

The 817S provides the basic necessities
for a home/office calculator -- it of course provides the four basic
math functions. It is a full-floating decimal machine, with eight
digit capacity. It has a single memory register, with a M+ (add to
memory), MR (memory recall), and MC(memory clear) key. It has a constant
function, which is enabled by the "K" key, which toggles constant mode on/off
which each depression. A "K" legend lights up in the display when the constant
is enabled. The constant function works for all four math functions.
It is clear that the same basic machine was offered with a "M-" key
to make it easier to subtract from memory. In the picture above, note
the 'empty' key location above the "M+" key. The keyboard on this machine
is 'modular', with a standard set of keys for zero through nine and
decimal point making up one 'module', and the other containing the
'functions'. A different 'function key' module, with an M- key
in the 'empty' location, along with a top cabinet
panel with an extra hole for the "M-" key and different model
number tag would make a 'higher power machine', and fetch a slightly
higher sales price, even though the electronics and manufacturing cost is
essentially identical.

Close up of 817S Circuitry

The Sharp ELSI (ELSI was an
acronym for "Extra Large Scale Integration")
817S is based on a single-chip LSI IC, part number 15331, made by Sharp.
A trio of Toshiba-made display driver chips make up the rest of the
IC's in the machine (2 TM4358, and 1 TM4352). The components are
placed on a single-sided phenolic circuit board, which uses jumpers
on the component side to make interconnections between traces on the
etch side of the board.

The Futaba-made Display Module

The display is a Futaba-made integrated
Vacuum Fluorescent display module, which plugs into the main board via an
edge-connector. The display module as 8 7-segment digit positions, and
a ninth position at the right end which has indicators for memory having
non-zero content (I), negative number (-), and constant mode active (K).
A green filter in the top part of the case turns blue glow of the
VF display into green digits as presented to the user.
The calculator uses a linear power supply with zener-diode based
voltage regulation. The keyboard modules use 'spring'-type contacts.

The 817S is fast, but since it's so
simple, it is really no surprise. 99999999 divided by 1 takes just
a blink of an eye. Overflow or invalid operations (divide by zero)
lock the machine with all digit positions showing '0' and all decimal
points turned on. A single press of the "C" key clears the error,
leaving 0 on the display. In non-error conditions, one press of the "C"
key clears the display, with a second press clearing the whole machine
(except for the memory register).